This invention relates to apparatus for, and a method of, measuring signal quality, and in particular to signal strength measurement in a piconet.
Short-range wireless networks (known as piconets) are used to interconnect mobile phones, computers and personal digital assistants (PDAs) with each other, and with home and business telephones using a short-range wireless connection. One well known protocol of this type is the Bluetooth protocol which operates at 2.45 Ghz. The maximum range of Bluetooth is 10 m, and data can be exchanged at a rate of 1 megabits per second (later generations will run at higher data rates). With Bluetooth, a piconet can support up to eight simultaneous devices, namely one master unit and seven slave units. This type of piconet can dynamically change as users enter and leave the range of the Bluetooth master unit.
Another known short-range wireless protocol is the wireless networking protocol IEEE802.11. Devices constructed in accordance with this protocol operate at 2.45 GHz, and a piconet can support a very large number of users. As with the Bluetooth, such a piconet can dynamically change as users enter and leave the piconet.
In order to co-ordinate such an ad-hoc network, it is desirable that prior notification is given of a network member""s intention to leave the network, so that any necessary changes in the management of the network can be made prior to the departure of that member. This is particularly important where members of a piconet share each others wide area network (WAN) interfaces in a co-ordinated fashion to obtain a single, logical, higher-speed WAN connection. An example of this is the streaming of video to a single user of a piconet by utilising the WAN connections of a number of other members of the piconet. This application is described in the specification of our co-pending U.S. patent application Ser. No. 09/809,427, filed Mar. 16, 2001, incorporated herein in its entirety by reference.
One way of determining whether a network member intends to leave the network is to measure the strength of signals received from that member. Thus, where the received signal strength from such a network member continually decreases towards the point of non-reception, it can be surmised by other members of the network that that member is intending to leave. Unfortunately, received signal strength depends on the propagation path of that signal and the environment, and this can vary considerably, particularly in a piconet. This is particularly the case where the piconet is positioned within a room, where the walls can give rise to spurious reflected signals. In such a situation, it is quite possible that one network member will receive signals from another network member which gradually decrease, even though that member is not intending to leave the network, the continually decreasing signal strength arising because of the relevant propagation path and the environment concerned.
The aim of the invention is to provide a method of measuring signal quality (such as signal strength) which gives a more reliable measurement of the signal quality concerned.
The present invention provides a method of measuring a signal quality parameter in a wireless network supporting a plurality of network user devices, the method comprising the steps of:
each user device measures a predetermined signal quality parameter of signals received from each of the other user devices in the network;
each user device broadcasts the measurements so made to said other user devices; and
each user device calculates, for each of the other user devices, a value for the predetermined signal quality parameter from all the received measurements associated with that other user device.
In a preferred embodiment, wherein the network is a short-range network, each user device has a receiver and a transmitter for short-range communication with the other user devices, and a processor for calculating said values.
Advantageously, the signal quality parameter is the signal strength, and each user device includes a combiner for combining the plurality of measurements associated with each of the other user devices. Preferably, each user device is such as to calculate the average of the plurality of measurements associated with each of the other user devices.
In a preferred embodiment, the method further comprises the step of determining that any given user device is about to leave the network by comparing said value of the signal strength of that user with a predetermined low level signal strength.
The invention also provides a wireless communications device comprising a transmitter, a receiver, a processor, an arrangement for measuring a signal quality parameter of signals received from other wireless communication devices, and a combiner arrangement for calculating a value for said parameter, for each of a plurality of said other communications devices, from the measurements so made and from other measurements of that parameter of that communications device made by said other communication devices and received by said receiver.
Advantageously, the transmitter and the receiver are short-range devices, and preferably form part of a Bluetooth transceiver.
In a preferred embodiment, the measuring arrangement includes a detector for measuring the strength of signals received.
The invention further provides a method of managing a wireless network supporting a plurality of network user devices, the method comprising the steps of:
at each user device, measuring a predetermined signal quality parameter of signals received from each of the other user devices in the network;
at each user device, broadcasting the measurements so made to said other user devices; and
managing the network using the broadcast measurements.